1. Technical Field
Exemplary embodiments of the present invention relate to a method for diagnosing a fault of a fuel cell stack.
2. Description of the Related Art
A fuel cell is a kind of power generating device that does not convert chemical energy of a fuel into heat by combustion, but converts the chemical energy into electrical energy by an electrochemical reaction in a stack and may be used to supply power to a small electric/electrical product, particularly, a portable apparatus as well as supply industrial power, home power, and power for driving a vehicle.
As a power supply for driving the vehicle, a polymer electrolyte membrane fuel cell (PEMFC) (proton exchange membrane fuel cell) having the highest power density among fuel cells has been currently studied mainly. The polymer electrolyte membrane fuel cell has a rapid start time due to a low operation temperature and a rapid power conversion reacting time.
The polymer electrolyte membrane fuel cell is configured to include a membrane electrode assembly (MEA) in which catalyst electrode layers in which an electrochemical reaction occur are attached to both sides of a solid polymer electrolyte membrane through which hydrogen ions move, a gas diffusion layer (GLD) serving to uniformly distribute reaction gases and transfer generated electrical energy, a gasket and coupling mechanism maintaining air-tightness of the reaction gases and coolant and appropriate coupling pressure, and a bipolar plate moving the reaction gases and the coolant.
When a fuel cell stack is assembled using the configuration of a unit cell as described above, a combination of the membrane electrode assembly and the gas diffusion layer, which are main components, is positioned in the innermost portion of the cell, the membrane electrode assembly includes the catalyst electrode layers, that is, an anode and a cathode, formed on both surfaces of the polymer electrolyte membrane and having catalysts applied thereto so that oxygen and hydrogen may react to each other, and the gas diffusion layer, the gasket, and the like, are stacked on outer sides of the anode and the cathode.
The bipolar plate provided with a flow field supplying the reaction gases (hydrogen, which is a fuel, and oxygen or air, which is an oxidizer) and passing the coolant therethrough is positioned at an outer side of the gas diffusion layer.
After a plurality of unit cells each having the above-mentioned configuration are stacked, a current collector, an insulating plate, and end plates supporting the stacked unit cells are coupled to the outermost portion. The unit cells are repeatedly stacked and coupled to each other between the end plates to configure the fuel cell stack.
In order to obtain potential actually required in the vehicle, the unit cells should be stacked by the required potential, and a product formed by stacking the unit cells is called a stack. Potential generated by one unit cell is about 1.3V. Therefore, a plurality of cells are stacked in series with each other in order to generate power required for driving the vehicle.
Meanwhile, in a fuel cell vehicle, a voltage of a cell is used to detect performance, an operation state, a fault, and the like, of a stack, and is used for various controls of a system such as a flow rate control of reaction gas. Typically, the bipolar plate is connected to a cell voltage monitoring apparatus through a connector and a conducting wire to monitor the voltage of the cell.
A cell voltage monitoring (CVM) apparatus according to the related art, which directly monitors voltages of all cells or two cells in the stack, uses a scheme in which a main controller (host controller) collecting voltages of all cells integrates and processes monitoring information and a voltage drop generated due to a fault result rather than a fault cause is monitored.
The cell voltage monitoring apparatus as described above has also been used to monitor a battery. Since the cell voltage monitoring apparatus according to the related art directly monitors the voltages of the cells, a position of a fault cell may be monitored. However, since the cell voltage monitoring apparatus according to the related art has a very complicated circuit configuration, it may be difficult to assemble and maintain the cell voltage monitoring apparatus according to the related art. In addition, the cell voltage monitoring apparatus according to the related art is expensive and may not detect a fault cause of the stack.
Further, an electrochemical impedance spectroscopy (EIS) has been used as the related art. The EIS is mainly used to detect an electrode reaction or a feature of a complex in an electrochemical field. The EIS may obtain general information on a nature, a structure, and a reaction of the complex by analyzing a system response and has also been used as a very useful tool in an applied chemistry field, a medical engineering field, a bioengineering field, or the like.
However, the EIS, which is for an off-line, requires a long test time, may not perform real-time monitoring, is expensive, and may be used only for testing a unit cell.